The purpose of the research proposed is to assess the joint roles of ecology and phyletic history in the evolution of neocortex. The hedgehog is selected as a mammalian prototype because its cortex is simple and consists of only a few subdivisions, most of which are sensory. An ablation study is proposed with the hypothesis that sensory cortex, when it first appears in mammalian history, does not serve simple sensory functions. The cortex of cats, squirrels, tree shrews (Tupaia glis) and bushbabies (Galago senegalensis) will be studied by anatomical, electrophysiological and behavioral methods. If similar cortical areas evolve in distantly related and dissimilar groups, then perhaps we can deduce some general behavioral achievement which is adaptive in a variety of niches. Comparisons between the tree shrew and squirrel should afford instances of the convergent evolution of cortex. Comparisons between the tree shrew and bushbaby, it is hoped, will shed light on the evolution of the temporal lobe in primates, including man. Comparisons between bushbaby and cat could provide an example of divergence, especially in the temporal lobe, since the cat's temporal cortex is so dominated by projections from the medial geniculate, while the evolution of the primate line is characterized by an expanding pulvinar target -- presumably related to vision. At the same time the bushbaby, like the cat, is nocturnal and very alert to sound.